1. Field of the Invention
The present invention relates to flexible membrane connectors and more particularly concerns membrane test connectors that provide a micro scrubbing action.
2. Description of Related Art
A significant application of the present invention concerns test probe connectors for use in testing of integrated circuits, and therefore a discussion of prior test probe connectors will provide a background for description of this aspect of the invention.
Integrated circuit chips are manufactured with large numbers of identical circuits on a single wafer which ultimately are separately cut from the wafer for use. It is desirable to test each circuit individually to determine whether or not it functions as intended before separating it from the wafer. Additional testing of separated circuits may be desired in various stages in assembly of a circuit and the finished apparatus. Further testing may be accomplished after packaging a circuit, after placing it in a multi-chip module, and after disassembly of a multi-chip module to identify inoperable circuits.
Conventional testing involves a probe card that is provided with a large number of small tungsten blades or needles that are mechanically and electrically connected to a circuit board and act as test probe contacts. Electrical leads extend from the contacts to the outer edge of the board for connecting the probe card to testing circuitry. In use of the blades or needles, they are moved into engagement with pads on an integrated circuit to be tested. The motion preferably should be such that there is a slight scrubbing action that is required for breaking through oxidation coating that often covers an aluminum, tin or solder type contact. Thus, blades or needles will effectively slide along or scrub the surface of the pad by a small amount to break the oxide coating. This provides a good electrical connection so that signals can be read to determine the integrity of the circuit on the chip. Proper scrubbing action is important, but difficult to obtain.
Ends of the test needles or blades must all fall in the same plane in order to assure that each one makes electrical contact with a pad of the integrated circuit. This is accomplished by bending the blades or needles after they have been mounted on the probe card, which, is laborious and time consuming, and expensive. Even after such adjustment, the blades or needles tend to creep back toward their original position so that their adjusted locations are lost. This lost of adjustment also comes about from the pressure of the needles against the chips, aggravated by the desired scrubbing action used to assure penetration of an oxide coating. As a result, constant maintenance is necessary or the probe cards will not perform their intended function. Even when in proper adjustment, the needles cannot compensate for significant differences in the heights of the contact pads on the integrated circuit chips being tested. The close spacing necessary for testing some chips cannot be achieved with conventional needle contacts. The needles may apply excessive force against the chip so as to damage the chips or their contact pads. This problem is greatly magnified by the fact that a single chip may require testing at different stages in its assembly into a finished module and that each such testing step requires a scrubbing action. In fact, some specifications will limit the number of times that a single chip that can be tested in order to avoid excessive chip damage caused by the testing operation itself.
Improved testing arrangements are disclosed in a co-pending application Ser. No. 606,676 filed Oct. 31, 1990, now U.S. Pat. No. 5,148,103, by John Pasiecznik, Jr. for Method and Apparatus for Testing Integrated Circuits and in a co-pending application Ser. No. 752,422, filed Aug. 30, 1991, now U.S. Pat. No. 5,264,787, by Blake F. Woith and William R. Crumly for Rigid Flex Circuits with Raised Features as IC Test Probe. Both of these applications are assigned to the same assignee as that of this application and both are incorporated herein by reference as though fully set forth.
In the above identified application of John Pasiecznik, Jr., a flexible membrane is stretched across a rigid angular substrate and provided with raised features on one side which connect through circuit traces to a probe card that is in turn connected to the test circuitry. During use of the membrane probe for testing, the membrane is distorted by air pressure or equivalent arrangements and contact of the membrane with the integrated circuit under test deflects the membrane to insure that raised contacts formed on the membrane are pressed against the pads of the integrated circuit to provide a good electrical connection. There has been no satisfactory way to obtain an adequate wiping or scrubbing action with the membrane probe of the Pasiecznik patent application. Deflection of the membrane during testing is too small to create an effective scrubbing action. Although the membrane of the above identified co-pending Applications is initially stretched and will experience a relaxation of the stretch during a small amount of over travel motion that follows initial touchdown of the test probe contact with the IC chip, the stretch of this membrane is distributed over the entire area of the membrane. In a typical membrane, having a radius of about one inch, the membrane is normally stretched by deflecting it downwardly by about 0.035 inches. This increases the total length along the membrane from its outer perimeter to its center by about 0.0005 inches. If engagement with a wafer or IC chip under test employs a 0.017 inch over travel, as is common, the total length of the membrane from the outer diameter to its center decreases by 0.00025 inches during over travel. However, this change in length is distributed over the full one inch radius of the membrane and, accordingly, is insignificant at any given single test probe contact, and will provide no effective scrubbing action.
Some connectors have been designed to produce a scrubbing action by moving the connector contact features or so-called gold dots to introduce a wiping action that occurs during contact. This has involved complicated cam or wedge mechanisms that are unreliable or costly and difficult to maintain. Furthermore, reliable wiping action requires a relatively large motion for the wiping. This impacts upon desired density of the connectors, making it difficult to utilize a test probe having contacts that are sufficiently close to one another.
Accordingly, is an object of the present invention to provide membrane connectors that minimize or avoid above-mentioned problems.